The present invention relates to a laser-beam operated machining apparatus which performs machining operations with a high energy density laser beam. More particularly, the invention relates to a laser-beam operated machining apparatus in which the machining efficiency is much higher than that of a conventional apparatus.
A conventional laser-beam operated machining apparatus of the same general type to which the invention relates is depicted in FIG. 1, which shows a sectional view of portions thereof. In FIG. 1, reference number 1 designates a laser oscillator; 2, a laser beam outputted by the laser oscillator 1; 3, a mirror for reflecting the laser beam toward a machining section; 4, a focusing optical system, namely, a focusing lens, for focusing the laser beam to an energy density suitable for machining; and 5, a nozzle provided below the focusing optical system 4 for applying the laser beam 2 together with assist gas to a workpiece 7. The nozzle 5 has an assist gas supplying port 6 for supplying various assist gases separately according to the particular machining purpose at hand. The nozzle 5 is in the form of a reverse cone coaxial with the laser beam 2.
The operation of the apparatus in FIG. 1 will be described. The laser beam 2 emitted by the laser oscillator 1 is reflected by the mirror 3. The reflected laser beam 2 is focused by the focusing optical system 4 into a spot having a high energy density of typically 10.sup.6 to 10.sup.8 W/cm.sup.2. The spot is applied to the surface of the workpiece 7, thus cutting, welding or heating the latter. In this operation, the assist gas is supplied through the assist gas supplying port 6 to the nozzle 5 so that it is applied to the surface of the workpiece 7 in such a manner that its flow is coaxial with the laser beam.
In cutting a workpiece, O.sub.2 gas is usually employed as the assist gas. In this case, oxidation reaction heat is generated between the O.sub.2 gas and the workpiece and material of the workpiece rendered molten and removed accordingly. In welding or heating a workpiece, Ar gas is employed to protect the workpiece's surface from oxidation by the air.
As is apparent from the above description, machining a workpiece with a laser beam is advantageous in that, since the high energy density of the focused laser beam can be utilized to evaporate, melt or heat a workpiece quickly, the workpiece can be machined in various manners with high efficiency.
The absorption factor of a laser beam depends greatly on its wavelength. FIG. 2 indicates the reflectivities of a variety of mirror-finished materials with respect to rays of different wavelengths. For a CO.sub.2 laser beam having an infrared wavelength of 10.6 microns, the reflectivity for most materials is considerably large. Accordingly, with a CO.sub.2 laser beam with a power density in a range suitable for machining, a material such as steel of relatively low reflectivity (the reflectivity being about 90% for a mirror-finished surface and 60% for a rough machined surface) can be machined with high efficiency. However, a material such as aluminum or copper of high reflectivity (the reflectivity being of the order of 90% even for a rough machined surface) cannot be machined. Thus, the range of application of a CO.sub.2 beam to machining work is greatly limited.